feat(app): 数据层集成 — RemoteJournalRepository + ClassRepository + SSE 通知

数据层新增:
- RemoteJournalRepository: 日记 CRUD + 元素管理，通过 ApiClient 连接后端
- ClassRepository: 班级/主题/评语 API 操作（getMyClasses/joinClass/assignTopic/createComment）
- SseNotificationService: SSE 实时通知监听 + 自动重连 + 事件流
- ApiException: 统一 API 错误封装
- DTO: ClassMemberDto + TopicDto + CommentDto

设计:
- Repository 模式: 抽象接口 + 远程实现 + 内存实现
- SSE: Dio stream + SSE 协议解析 + 3秒自动重连
- 所有 Repository 通过 ApiClient 注入，依赖现有 JWT 拦截器

验证: flutter analyze 0 error

app/lib/data/repositories/class_repository.dart

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+// 班级仓库 — 通过 API 客户端管理班级、主题、评语
+
+import '../models/school_class.dart';
+import '../remote/api_client.dart';
+
+/// 班级成员数据
+class ClassMemberDto {
+  final String userId;
+  final String role;
+  final String? nickname;
+  final DateTime joinedAt;
+
+  const ClassMemberDto({
+    required this.userId,
+    required this.role,
+    this.nickname,
+    required this.joinedAt,
+  });
+
+  factory ClassMemberDto.fromJson(Map<String, dynamic> json) => ClassMemberDto(
+        userId: json['user_id'] as String,
+        role: json['role'] as String,
+        nickname: json['nickname'] as String?,
+        joinedAt: DateTime.parse(json['joined_at'] as String),
+      );
+}
+
+/// 主题布置数据
+class TopicDto {
+  final String id;
+  final String classId;
+  final String teacherId;
+  final String title;
+  final String? description;
+  final DateTime? dueDate;
+  final bool isActive;
+
+  const TopicDto({
+    required this.id,
+    required this.classId,
+    required this.teacherId,
+    required this.title,
+    this.description,
+    this.dueDate,
+    this.isActive = true,
+  });
+
+  factory TopicDto.fromJson(Map<String, dynamic> json) => TopicDto(
+        id: json['id'] as String,
+        classId: json['class_id'] as String,
+        teacherId: json['teacher_id'] as String,
+        title: json['title'] as String,
+        description: json['description'] as String?,
+        dueDate: json['due_date'] != null
+            ? DateTime.parse(json['due_date'] as String)
+            : null,
+        isActive: (json['is_active'] as bool?) ?? true,
+      );
+}
+
+/// 评语数据
+class CommentDto {
+  final String id;
+  final String journalId;
+  final String authorId;
+  final String content;
+  final DateTime createdAt;
+
+  const CommentDto({
+    required this.id,
+    required this.journalId,
+    required this.authorId,
+    required this.content,
+    required this.createdAt,
+  });
+
+  factory CommentDto.fromJson(Map<String, dynamic> json) => CommentDto(
+        id: json['id'] as String,
+        journalId: json['journal_id'] as String,
+        authorId: json['author_id'] as String,
+        content: json['content'] as String,
+        createdAt: DateTime.parse(json['created_at'] as String),
+      );
+}
+
+/// 班级仓库 — 班级/主题/评语的 API 操作
+class ClassRepository {
+  final ApiClient _api;
+
+  ClassRepository({required ApiClient api}) : _api = api;
+
+  // ===== 班级 =====
+
+  /// 获取我加入的班级列表
+  Future<List<SchoolClass>> getMyClasses() async {
+    final response = await _api.get('/diary/classes');
+    final body = response.data as Map<String, dynamic>;
+    final items = body['data'] as List? ?? [];
+    return items
+        .map((json) => SchoolClass.fromJson(json as Map<String, dynamic>))
+        .toList();
+  }
+
+  /// 创建班级（老师）
+  Future<SchoolClass> createClass({
+    required String name,
+    String? schoolName,
+  }) async {
+    final response = await _api.post('/diary/classes', data: {
+      'name': name,
+      if (schoolName != null) 'school_name': schoolName,
+    });
+    final body = response.data as Map<String, dynamic>;
+    return SchoolClass.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  /// 加入班级（通过班级码）
+  Future<SchoolClass> joinClass(String classCode, {String? nickname}) async {
+    final response = await _api.post('/diary/classes/join', data: {
+      'class_code': classCode,
+      if (nickname != null) 'nickname': nickname,
+    });
+    final body = response.data as Map<String, dynamic>;
+    return SchoolClass.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  /// 获取班级详情
+  Future<SchoolClass> getClass(String classId) async {
+    final response = await _api.get('/diary/classes/$classId');
+    final body = response.data as Map<String, dynamic>;
+    return SchoolClass.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  /// 获取班级成员列表
+  Future<List<ClassMemberDto>> getMembers(String classId) async {
+    final response = await _api.get('/diary/classes/$classId/members');
+    final body = response.data as Map<String, dynamic>;
+    final items = body['data'] as List? ?? [];
+    return items
+        .map((json) => ClassMemberDto.fromJson(json as Map<String, dynamic>))
+        .toList();
+  }
+
+  // ===== 主题 =====
+
+  /// 获取班级主题列表
+  Future<List<TopicDto>> getTopics(String classId) async {
+    final response = await _api.get('/diary/classes/$classId/topics');
+    final body = response.data as Map<String, dynamic>;
+    final items = body['data'] as List? ?? [];
+    return items
+        .map((json) => TopicDto.fromJson(json as Map<String, dynamic>))
+        .toList();
+  }
+
+  /// 布置主题（老师）
+  Future<TopicDto> assignTopic({
+    required String classId,
+    required String title,
+    String? description,
+    DateTime? dueDate,
+  }) async {
+    final response = await _api.post('/diary/classes/$classId/topics', data: {
+      'title': title,
+      if (description != null) 'description': description,
+      if (dueDate != null) 'due_date': dueDate.toIso8601String(),
+    });
+    final body = response.data as Map<String, dynamic>;
+    return TopicDto.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  // ===== 评语 =====
+
+  /// 获取日记评语列表
+  Future<List<CommentDto>> getComments(String journalId) async {
+    final response = await _api.get('/diary/journals/$journalId/comments');
+    final body = response.data as Map<String, dynamic>;
+    final items = body['data'] as List? ?? [];
+    return items
+        .map((json) => CommentDto.fromJson(json as Map<String, dynamic>))
+        .toList();
+  }
+
+  /// 添加评语（老师点评学生日记）
+  Future<CommentDto> createComment({
+    required String journalId,
+    required String content,
+  }) async {
+    final response = await _api.post(
+      '/diary/journals/$journalId/comments',
+      data: {'content': content},
+    );
+    final body = response.data as Map<String, dynamic>;
+    return CommentDto.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  /// 删除评语
+  Future<void> deleteComment(String commentId) async {
+    await _api.delete('/diary/comments/$commentId');
+  }
+}

app/lib/data/repositories/remote_journal_repository.dart

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+// 远程日记仓库 — 通过 API 客户端连接后端
+
+import '../models/journal_element.dart';
+import '../models/journal_entry.dart';
+import '../remote/api_client.dart';
+import 'journal_repository.dart';
+
+/// 远程日记仓库 — 通过 HTTP API 操作后端数据
+///
+/// 所有操作需要网络连接。离线场景由 SyncEngine 协调 Isar 本地仓库处理。
+class RemoteJournalRepository implements JournalRepository {
+  final ApiClient _api;
+
+  RemoteJournalRepository({required ApiClient api}) : _api = api;
+
+  @override
+  Future<List<JournalEntry>> getJournals({
+    DateTime? dateFrom,
+    DateTime? dateTo,
+    int? page,
+    int? pageSize,
+  }) async {
+    final queryParams = <String, dynamic>{};
+    if (dateFrom != null) queryParams['date_from'] = dateFrom.toIso8601String();
+    if (dateTo != null) queryParams['date_to'] = dateTo.toIso8601String();
+    if (page != null) queryParams['page'] = page;
+    if (pageSize != null) queryParams['page_size'] = pageSize;
+
+    final response = await _api.get('/diary/journals', queryParams: queryParams);
+    final body = response.data as Map<String, dynamic>;
+    final items = body['data'] as List? ?? [];
+    return items
+        .map((json) => JournalEntry.fromJson(json as Map<String, dynamic>))
+        .toList();
+  }
+
+  @override
+  Future<JournalEntry?> getJournal(String id) async {
+    try {
+      final response = await _api.get('/diary/journals/$id');
+      final body = response.data as Map<String, dynamic>;
+      return JournalEntry.fromJson(body['data'] as Map<String, dynamic>);
+    } on ApiException catch (e) {
+      if (e.statusCode == 404) return null;
+      rethrow;
+    }
+  }
+
+  @override
+  Future<JournalEntry> createJournal(JournalEntry entry) async {
+    final response = await _api.post('/diary/journals', data: entry.toJson());
+    final body = response.data as Map<String, dynamic>;
+    return JournalEntry.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  @override
+  Future<JournalEntry> updateJournal(JournalEntry entry) async {
+    final response = await _api.put(
+      '/diary/journals/${entry.id}',
+      data: {
+        'title': entry.title,
+        'mood': entry.mood.value,
+        'weather': entry.weather.value,
+        'tags': entry.tags,
+        'is_private': entry.isPrivate,
+        'shared_to_class': entry.sharedToClass,
+        'version': entry.version,
+      },
+    );
+    final body = response.data as Map<String, dynamic>;
+    return JournalEntry.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  @override
+  Future<void> deleteJournal(String id) async {
+    await _api.delete('/diary/journals/$id');
+  }
+
+  @override
+  Future<List<JournalElement>> getElements(String journalId) async {
+    final response = await _api.get('/diary/journals/$journalId/elements');
+    final body = response.data as Map<String, dynamic>;
+    final items = body['data'] as List? ?? [];
+    return items
+        .map((json) => JournalElement.fromJson(json as Map<String, dynamic>))
+        .toList();
+  }
+
+  @override
+  Future<JournalElement> addElement(JournalElement element) async {
+    final response = await _api.post(
+      '/diary/journals/${element.journalId}/elements',
+      data: element.toJson(),
+    );
+    final body = response.data as Map<String, dynamic>;
+    return JournalElement.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  @override
+  Future<JournalElement> updateElement(JournalElement element) async {
+    final response = await _api.put(
+      '/diary/journals/${element.journalId}/elements/${element.id}',
+      data: element.toJson(),
+    );
+    final body = response.data as Map<String, dynamic>;
+    return JournalElement.fromJson(body['data'] as Map<String, dynamic>);
+  }
+
+  @override
+  Future<void> removeElement(String elementId) async {
+    await _api.delete('/diary/elements/$elementId');
+  }
+}
+
+/// API 异常封装 — 后端返回非 2xx 状态码时抛出
+class ApiException implements Exception {
+  final String message;
+  final int statusCode;
+  final dynamic responseBody;
+
+  const ApiException({
+    required this.message,
+    required this.statusCode,
+    this.responseBody,
+  });
+
+  @override
+  String toString() => 'ApiException($statusCode): $message';
+}

app/lib/data/services/sse_notification_service.dart

@@ -0,0 +1,146 @@
+// SSE 通知服务 — 监听服务端推送事件
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:dio/dio.dart';
+
+/// SSE 通知事件
+class NotificationEvent {
+  final String type;
+  final Map<String, dynamic> payload;
+  final DateTime receivedAt;
+
+  const NotificationEvent({
+    required this.type,
+    required this.payload,
+    required this.receivedAt,
+  });
+}
+
+/// SSE 通知服务 — 监听后端 Server-Sent Events 推送
+///
+/// 使用方式：
+/// ```dart
+/// final service = SseNotificationService(token: 'jwt-token');
+/// service.events.listen((event) {
+///   // 处理通知
+/// });
+/// await service.connect();
+/// ```
+class SseNotificationService {
+  final String _baseUrl;
+  final String? _token;
+
+  Dio? _dio;
+  Response<ResponseBody>? _response;
+  StreamController<NotificationEvent>? _controller;
+  bool _disposed = false;
+
+  SseNotificationService({
+    required String token,
+    String baseUrl = 'http://localhost:8080/api/v1',
+  })  : _token = token,
+        _baseUrl = baseUrl;
+
+  /// 通知事件流
+  Stream<NotificationEvent> get events {
+    _controller ??= StreamController<NotificationEvent>.broadcast();
+    return _controller!.stream;
+  }
+
+  /// 连接到 SSE 端点
+  Future<void> connect() async {
+    if (_disposed) return;
+
+    _dio = Dio(BaseOptions(
+      baseUrl: _baseUrl,
+      headers: {
+        'Accept': 'text/event-stream',
+        'Cache-Control': 'no-cache',
+        if (_token != null) 'Authorization': 'Bearer $_token',
+      },
+      responseType: ResponseType.stream,
+    ));
+
+    try {
+      _response = await _dio!.get<ResponseBody>('/message/stream');
+
+      if (_response?.data == null) return;
+
+      _response!.data!.stream.listen(
+        (data) {
+          _parseSseData(data);
+        },
+        onError: (error) {
+          if (!_disposed) {
+            // 自动重连逻辑（3秒延迟）
+            Future.delayed(const Duration(seconds: 3), () {
+              if (!_disposed) connect();
+            });
+          }
+        },
+        onDone: () {
+          if (!_disposed) {
+            Future.delayed(const Duration(seconds: 3), () {
+              if (!_disposed) connect();
+            });
+          }
+        },
+      );
+    } catch (e) {
+      // 连接失败，延迟重连
+      if (!_disposed) {
+        Future.delayed(const Duration(seconds: 5), () {
+          if (!_disposed) connect();
+        });
+      }
+    }
+  }
+
+  /// 解析 SSE 数据帧
+  void _parseSseData(List<int> data) {
+    final text = utf8.decode(data);
+    final lines = text.split('\n');
+
+    String? eventType;
+    String? eventData;
+
+    for (final line in lines) {
+      if (line.startsWith('event:')) {
+        eventType = line.substring(6).trim();
+      } else if (line.startsWith('data:')) {
+        eventData = line.substring(5).trim();
+      } else if (line.isEmpty && eventType != null && eventData != null) {
+        // 空行 = 事件结束
+        _emitEvent(eventType, eventData);
+        eventType = null;
+        eventData = null;
+      }
+    }
+  }
+
+  /// 发射通知事件到流
+  void _emitEvent(String type, String data) {
+    if (_disposed || _controller == null) return;
+
+    try {
+      final payload = jsonDecode(data) as Map<String, dynamic>;
+      _controller!.add(NotificationEvent(
+        type: type,
+        payload: payload,
+        receivedAt: DateTime.now(),
+      ));
+    } catch (_) {
+      // 忽略解析错误
+    }
+  }
+
+  /// 断开连接并释放资源
+  void dispose() {
+    _disposed = true;
+    _response?.data?.stream.listen((_) {});
+    _controller?.close();
+    _dio?.close();
+  }
+}